The present invention relates to a load cell and particularly to a load-sensing system of the type where a load carrier is supported by a load cell for sensing the load on the carrier. Such load cells and load-sensing systems may be used for various purposes, and for exemplary purposes are disclosed herein in a weighing system, such as for the weighing of trucks or railway cars.
Load-sensing systems which are employed in weighing of vehicles, such as trucks and railroad cars, include load cells which measure the load on a load carrier. Such systems may be found in U.S. Pat. Nos. 3,714,997; 3,734,216; 3,734,217; and 3,741,327. These patents disclose systems which eliminate the need for massive foundation supports (which are cumbersome, time-consuming, and expensive to install) by providing vehicle weighing devices which are supported for movement with the rails and which may be easily but, yet, accurately installed in existing railway systems. These systems include a load carrier onto which the vehicle is moved. The load carrier is supported by a plurality of load cells.
One problem that exists in the design of weighing systems is the problem of accuracy. The load must be applied to the load-sensing cell in the proper direction to obtain accurate weighing. For example, in vehicle scales the movement of the vehicle (load being weighed) onto the load carrier tends to cause movement of the load carrier relative to the load-sensing cell, which tendency affects the accuracy of the weighing system. If the load carrier was allowed to move so far that it hit the pit walls the load would be shunted past the load cells, resulting in erroneous readings. The common manner of solving this problem is to use check rods to limit load carrier shifting. U.S. Pat. No. 3,736,998 also solves this problem by using a linkage intermediate the load carrier and a load sensing-cell which provides for proper application of the load to the load cell, even though the load carrier may shift.
In addition, accuracy in such weighing systems is affected by the construction of the load cell or cells used in the system. With respect to shear beam load cells, the position of the strain gauges on the shear beam is critical to accuracy, particularly if the load cell is to accept side loads or twisting moments. Theoretically, if the strain gauges are precisely positioned the affect on one side of the shear beam cancels the affect on the other side of the beam. However, such precise perfect positioning is difficult if not impossible as a practical matter to obtain.